Old Ebbitt Grill serves oysters from five to six different locales at any given time.

Maggie StarbardNPR

Despite its proximity to the Chesapeake Bay, Washington, D.C. isn't a seafood town in its own right, with a proper port. But just steps away from the White House, in the most straight-laced section of a straight-laced town, is a kind of temple to the most sensual of seafood – the raw oyster.

Old Ebbitt Grill, founded in 1856, sells an inordinate amount of oysters every year – the total was 985,000 in 2010, according to the restaurant's purchaser — more than almost any other restaurant on the East Coast.

But what's surprising is how much of the shucking and slurping happens in the wee, dark hours of night. Since 1996, the restaurant has featured a late night oyster happy hour, where seasonal oysters harvested from the coldest Atlantic and Pacific waters sell at half price from 11pm to 1am and the wood-paneled restaurant's four bars are alive with chatter and the clinking of ice and shell. The pull of late-night oysters has proven so successful for the Ebbitt that other local restaurants, from Hank's Oyster Bar to Blackbyrd Warehouse, recently announced they're following suit.

While Washingtonians seem to have a special appreciation for late night oysters, they can also be found in select oyster bars from New York to Seattle. So what exactly is their pull, aside from a happy hour discount? (The agreeable price, by the way, doesn't seem to have much to do with the oysters' freshness.)

It turns out Americans have sought out midnight oysters for centuries, for their convenience, their lightness, and their mischievous reputation. Whatever the appeal, the salty late night snack flaunting flavor over bulk endures.

Mark Kurlansky, author of The Big Oyster: History on the Half Shell, tells The Salt that in 19th-century New York, oysters were a food of the night thanks to the practice of "whoring in the slums — the rumor of an aphrodisiac." Men in search of lewd women and briny flavors could dine on discounted oysters at oyster cellars lit by red globes; 6 cents got you all you could eat. More prudish New Yorkers might have visited the huge open air downtown markets as they waited for the night ferries to Brooklyn. "It was a custom to stop off and have a few oysters before hopping a ferry home," Kurlansky says.

Another oyster scholar says today's nighttime oyster eaters are a distinct and cultivated breed, perhaps tempted by their naughty legacy. "Who out there is eating raw oysters? ... It's the experimenters, the explorers, the risk takers, the people who want to know the world and all the things it has to offer. It's borderline taboo, so only taboo-breakers need apply ... Just go to an oyster bar, look around, and know that you are among the other sensualists, those who love delight and aren't bashful about embracing it," writes Rowan Jacobson in A Geography of Oysters: The Connoisseur's Guide to Oyster Eating in North America.

The story behind the Ebbitt's late night oyster happy hour is partly one of smart business sense. Managing director David Moran tells us that when the restaurant decided to bring back its oyster program in 1996, he had the idea to have two happy hours, one early and one late. "Little did we know that the late one would be the popular end," says Moran.

It started with restaurant waiters and cooks who were getting off work late. Then they invited their friends. At some point, the restaurant earned a reputation as a place that knew its oysters and went the extra mile to source high quality. (All oysters served there have been tested for harmful bacteria at an independent lab.) The clientele also became more sophisticated; today, the average oyster diner at the grill has a well-formed opinion on what are the best oyster waters in the world.

The Ebbitt currently offers a selection of around five oysters at any given time – this month they're from four different sites around Prince Edward Island in Canada, and one in Buzzard's Bay in Massachusetts. On a recent visit, our party of three decided that the Massachusetts oyster had the nicest combination of sweet and salt.

Since the Ebbitt prefers oysters from cold, wintry waters, its oyster season is really just getting started. Come November, oyster fanatics can guzzle 25 varieties at the annual Oyster Riot. But alas, the event ends at 9:30pm — well before the late-night connoisseurs even get started.